Dresden 2003 – wissenschaftliches Programm
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TT: Tiefe Temperaturen
TT 4: Schwere Fermionen, Kondo-Systeme
TT 4.5: Vortrag
Montag, 24. März 2003, 15:45–16:00, HSZ03
Study of the magnetic order in CeCu2(Si1−xGex)2: evidence for a critical point at x=0.25 — •M. Deppe, R. Borth, C. Geibel, P. Hinze, N. Oeschler, O. Stockert, and F. Steglich — Max-Planck-Institute for Chemical Physics of Solids, Nöthnitzer Str. 40, 01187 Dresden, Germany
In heavy-fermion systems the Kondo-temperature TK is the dominant energy scale. At lower TK values, the Kondo interaction becomes weaker than the intersite RKKY exchange, leading to a competition between Kondo screening and magnetic order. We have investigate this competition in the alloy CeCu2(Si1−xGex)2 by means of specific heat Cp(T), thermal expansion α(T) and resistivity measurements on single crystals. Elastic neutron - scattering experiments on single crystals showed antiferromagnetic order with a propagationvector q = (0.28, 0.28, 0.51) at x = 0.5. This type of antiferromagnetic order is visible up to a Germanium content of x=0.05. The observed magnetic moment decreases strongly with x, indicating a strong increase of the Kondo - temperature TK at low Germanium content. Analysis of our Cp(T) and α(T) results suggest that this increase is non monotonic, being much more pronounced near x=0.25. Further on, at this concentration, four phase boundaries between different magnetic states merge. This suggest that the composition x=0.25 corresponds to a critical point, where the increasing competition between Kondo-screening and RKKY interaction induces changes in the ordered magnetic structure. These results shall be discussed in the context of models proposed for local- and spin-density-wave critical points.